Although it is known that the biochemical and physiological characteristics of the muscle fiber types in the laryngeal muscels of animal models differ from those of the limb muscles, little is known about the muscle fibers in the human laryngeal muscles. Since muscle fiber characteristics are generally considered to be mainly a function of motor unit activity patterns, the muscle fiber types in the human larynx might be expected to differ from those of animals due to the highly developed capacity for vocalization in man. In the proposed investigation quantitiative histochemical and morphometric techniques will be used to examine the biochemical and ultrastructural characteristics of the various muscle fiber types in the human and cat laryngeal muscles. By referencing the position of each fiber to various anatomical landmarks through the use of computer-interfaced linear potentiometers mounted on the microscope stage, it will be possible to determine the overall architectrual organization of the muscle fiber type mosaic. This quantitative data concerning the biochemical and ultrastructural architecture of these muscles will increase our understanding of laryngeal function. The relationship between the sex and age of the individual and the muscle fiber characteristics will also be examined since these variables have been reported to determine characteristics of muscle fibers in other human muscles. Our preliminary studies have suggested a high frequency of partial denervation followed by reinnervation (muscle fiber "type grouping") in the human posterior cricoarytenoid muscle by the fifth decade of life. Therefore the use of these quantitative histochemical and ultrastructural techniques to examined age-related changes in the laryngeal muscles will be of special interest. Since this indicates an increase in motor unit sizes these pathological changes would result in more coarsely controlled muscles and in this way alter laryngeal function.